In the related art, a mass spectrometer that uses a quadrupole type mass spectrometer is formed from at least four rod-shaped electrodes, in which a DC voltage U and a high-frequency voltage Vqcos (Ωqt+ϕ0) are applied to the rod-shaped electrodes. There are many cases in which an ion transport part (an ion guide part), formed from at least four rod-shaped or plate-shaped electrodes, and in which only a high-frequency voltage Vicos (Ωit+ϕ0) is applied, is installed separately from a mass spectrometry part. Such an ion transport part performs mass selection of and separates ion types having specific mass-to-charge ratios m/z in a stage prior to the mass spectrometry part in order to decrease ion loss when an ion beam from a test piece is caused to be incident to the mass spectrometry part.
At this time, in a case where the radius of an inscribed circle, in which the shortest distance between opposing electrodes of the electrodes of the ion transport part is set as the diameter, is set as ri, and the radius of an inscribed circle, in which the shortest distance between opposing electrodes of the electrodes of the mass spectrometry part is set as the diameter, is set as rq, the ion transport part and the mass spectrometry part are disposed so that ri=rq. In addition, voltages are applied so that Vi=Vq and Ωi=Ωq. From this point onwards, an inscribed circle, in which the shortest distance between opposing electrodes is set as the diameter, will be referred to as an inscribed circle of rod-shaped electrodes.
In addition, in the manner disclosed in PTL 1, with respect to the electrodes of the ion transport part, the ion transport part electrodes being disposed so that a relationship of ri1>ri2 is established where the radius of an inscribed circle of rod-shaped electrodes in a position in which ions are incident to the ion transport part, is set as ri1, and the radius of an inscribed circle of rod-shaped electrodes in a position in which ions are emitted from the ion transport part, is set as ri2, is disclosed.